No wreckage, no clues... just endless questions

MYSTERIES: As the investigation into the MH370 plane deepens, more questions arise [GETTY]

No trace of the plane has been found five days later. Here we look at some of the clues to the stricken plane’s fate.

What do experts think happened to the plane?

Scores of theories include an explosive decompression, hijacking or a bomb blast. Lack of information has sparked fears of a military strike.

Why are some family members claiming their loved ones’ phones are still ringing?

This could mean the mobiles are on dry land and near a transmitter. However phones with no battery often seem to ring before going through to voicemail.

What about rumours the plane was forced to land at a secret location by Vietnamese fighter jets?

The Boeing 777 is a huge plane that would need a 2km runway to land. Pilot Robin Durie said: “You don’t just land a plane like that in a clearing in the jungle.”

Why has the plane’s black box not revealed the area where it landed?

Although black box recorders are almost indestructible, their transmitters have a very short range.

Why has no trace of the missing plane been found?

The jet had enough fuel to fly hundreds of miles out of current search areas.

“Hijackers may have turned off the transponder, which assists radar tracking”

Is it possible for a plane to vanish from radar completely?

Yes, including in dense and remote areas such as the Malaysian jungle.

Why didn’t the plane send out a distress signal?

If the airliner suddenly disintegrated in mid-air the pilots may not have had time to call. Hijackers may have turned off the transponder, which assists radar tracking. Robin added: “This suggests to me that whatever happened, happened really quickly.”

Could a deranged passenger have gained access to the cockpit?

Possibly, says aviation expert Philip Baum. He explained: “There’s a lot of complacency with flight deck doors. They are opened at various times throughout the flight.”

What about claims the plane descended rapidly and flew in the opposite direction?

Any such change could be a sign of a hijack or foul-play by a crew member. Robin said an emergency change of course is usually only by 90 degrees, and accompanied by a call to air traffic control.

A pilot nearby claimed he heard mumbling over the radio after the jet went missing, why?

It could be from another plane. However, it could be a sign that the crew had been starved of oxygen and were about to pass out.